During normal daily activity of a patient, medical device leads flex through a large number of cycles and withstand various other stresses. Numerous cycles of flexing causes fatigue damage and failure in leads, and other stresses such as axial stress can further cause lead damage. Leads are particularly susceptible to fatigue damage or failure at stress concentration points along the lead. Examples of stress concentration points include, but are not limited to where a lead exits a pulse generator, or where a lead is attached to a more rigid structure such as an electrode. Kinking in a flexural direction and crushing in a radial direction may also be problems in stress concentration points.
Leads may follow narrow and tortuous paths which may require short electrodes to navigate tight bends, thus creating more stress concentration points. Additionally, the designed size of leads is decreasing with industry pressure to make less invasive products. Smaller leads tend to be more fragile, which further increases the need for more robust lead designs that can withstand numerous flex cycles and axial stresses.